The invention relates to improvements in torque transmitting systems in general, and more particularly to improvements in torque transmitting systems which can be utilized in the power trains of motor vehicles, for example, to transmit torque between a prime mover (such as an internal combustion engine or a hybrid engine) and a manually operable or automated gearbox. Still more particularly, the invention relates to improvements in torque transmitting systems of the type known as hydrokinetic torque converters with bypass or lockup clutches.
As a rule, a hydrokinetic torque converter comprises a housing or casing which is connected to and can be rotated by the output element of a prime mover (such as the camshaft or crankshaft of a combustion engine), a pump which is mounted in and can be of one piece with the housing, a turbine which is confined in and coaxial with the housing and can rotate with as well as relative to the housing so that its hub can transmit torque to a rotary input element (e.g., a shaft) of the gearbox, an optional stator in the housing between the pump and the turbine, and a bypass or lockup clutch which can operate with as well as without slip so as to transmit torque between the housing and the turbine. The bypass clutch can comprise a piston which is movable axially of the housing in order to disengage, partially engage (with slip) or fully engage (without slip) the clutch so that the latter can transmit a selected torque between a portion of the housing and the hub of the turbine. The connection between the piston of the bypass clutch and the turbine can comprise one or more shock absorbing dampers, and the piston is movable axially by a pressurized fluid (e.g., oil) which is confined in the housing. To this end, the piston divides an internal chamber of the housing into two compartments or plenum chambers. If the fluid pressure in one of the compartments is raised above that in the other compartment, the piston can be moved axially of the housing from a position corresponding to a fully engaged condition of the bypass clutch, through a plurality of intermediate positions in which the clutch operates with slip, to a position corresponding to a fully disengaged condition of the clutch. Inversely, if the fluid pressure in the other compartment rises above that in the one compartment, the piston is moved axially of the housing in the opposite direction, i.e., to change the condition of the bypass clutch from the fully disengaged condition, through a desired number of partially engaged conditions (operation with a selected slip) and to the fully engaged condition.
The piston of the bypass clutch can be provided with a friction lining having an exposed friction surface which can contact, with or without slip (or move to a position entirely out of contact with), a complementary friction surface, e.g., directly on a section of the housing of the torque converter or on a friction lining which is affixed to the housing. It is also possible to employ a single friction lining which is bonded or otherwise affixed to the housing and has a friction surface arranged to contact a complementary friction surface on the piston of the bypass clutch.
It is also known to provide the friction surface of a friction lining, the friction surface of the piston of the bypass clutch, and/or the friction surface of the housing of the hydrokinetic torque converter with one or more channels for one or more fluid streams serving to withdraw heat from the bypass clutch and, if necessary, from certain other constituents of the torque converter and/or its bypass clutch (e.g., from the aforementioned damper or dampers). If the channel or channels is or are provided in a generally washer-like friction lining, each such channel can have an inlet in the radially inner or in the radially outer marginal portion and an outlet in the radially outer or in the radially inner marginal portion of such friction lining. Reference may be had to published German patent application Serial No. 1 950 0814 and to the corresponding United States patent(s) and/or patent application(s). The disclosure of each United States patent and of each allowed United States patent application mentioned in this specification is incorporated herein by reference.
Presently known torque converters of the above outlined character exhibit the drawback that the flow of fluid coolant along the friction surface(s) of the bypass clutch is not entirely satisfactory (predictable), for example, when the clutch operates with slip. Thus, if the fluid conveying channels or grooves extend in directions other than exactly or substantially radially of the piston and the bypass clutch operates with a certain amount of slip between the abutting friction surfaces (one of which is caused to rotate with the housing of the torque converter and the other of which is provided (directly or indirectly) on the piston), the normally viscous fluid flowing in the channels of one friction surface is maintained in frictional engagement with the other (complementary) friction surface to thus produce a retarding force (drag) which is proportional to the slip of the bypass clutch. This can exert an adverse influence upon the distribution of pressures at the bypass clutch, e.g., it can entail an undesired engagement of the bypass clutch with resulting considerable discomfort to the occupant or occupants of the motor vehicle in which the torque converter is put to use.
Another drawback of presently known hydrokinetic torque converters employing fluid-cooled bypass or lockup clutches is that the characteristics of the channels or grooves in the friction surface(s) are not selected with a view to prevent the development of eddy currents which affect the quality of the heat-withdrawing (cooling) action of the fluid medium in such channels or grooves.